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Minimal exclusion of plasma membrane proteins during retroviral envelope formation
M Hammarstedt1, K Wallengren, K W Pedersen
1Karolinska Institutet, Department of Biosciences at Novum, S-141 57 Huddinge, Sweden.
Abstract:
The retrovirus forms its envelope by budding at the plasma membrane (PM). This process is primarily driven by its cytoplasmic core-precursor protein, Gag, as shown by the efficient formation of virus-like Gag particles in the absence of its envelope protein, Env. Most interestingly, several studies have demonstrated incorporation of various PM proteins into retrovirus, but the underlying mechanism of this phenomenon has remained elusive. We have purified Moloney murine leukemia virus Gag particles by sedimentation in an iodixanol gradient and donor PMs by flotation in a sucrose gradient and compared their protein compositions at equal lipid basis. We found that most PM proteins are present at similar density in both membranes. The inclusion of PM proteins was unaffected by incorporation of Env protein into the envelope of the Gag particles and whether these were produced at high or low level in the cells. These findings indicate that most PM proteins become incorporated into the retrovirus envelope without significant sorting. This feature of retrovirus assembly should be considered when studying retrovirus functions and developing retrovirus vectors.
Insights
Retrovirus assembly incorporates most plasma membrane proteins without sorting. This occurs independently of envelope proteins and production levels, impacting retrovirus function studies and vector development.
Area of Science:
- Virology
- Cell Biology
- Biochemistry
Background:
- Retroviruses bud from the plasma membrane, a process driven by the Gag protein.
- Incorporation of plasma membrane proteins into retroviruses is observed but mechanistically unexplained.
Purpose of the Study:
- To investigate the mechanism of plasma membrane protein incorporation into retrovirus particles.
- To compare protein composition of retroviral Gag particles and plasma membranes.
Main Methods:
- Purification of Moloney murine leukemia virus Gag particles via iodixanol gradient sedimentation.
- Purification of donor plasma membranes through sucrose gradient flotation.
- Comparative proteomic analysis based on equal lipid quantities.
Main Results:
- Most plasma membrane proteins exhibit similar densities in both purified Gag particles and plasma membranes.
- Plasma membrane protein incorporation is independent of envelope (Env) protein presence.
- Protein incorporation levels are unaffected by Gag particle production rates.
Conclusions:
- Retrovirus assembly incorporates a broad range of plasma membrane proteins without significant selective sorting.
- This non-selective incorporation mechanism is a key consideration for understanding retrovirus biology and engineering retroviral vectors.